Treatment of opioid use disorder (OUD) with buprenorphine (BUP) has significant individual and societal benefits, and decreases the risk of death from overdose. Yet, few individuals have access to these treatments. Narrowing the treatment gap by expanding access to treatment in Emergency Department (ED) settings is widely viewed to be a public health priority. It has been 3 years since D?Onofrio et al.?s landmark paper demonstrated the feasibility, safety, and efficacy of ED-initiated BUP, and, despite a highly visible opioid epidemic, few EDs have adopted this life-saving intervention. Coincident with the intensifying opioid epidemic, there have been increasing calls for development and use of quality measures to track and improve the quality of care for OUD and implement policy strategies to identify and incentivize use of best practices. Through our work, including leading two ongoing NIDA Clinical Trials Network multicenter studies of the implementation and effectiveness of ED-initiated BUP and referral, our team has identified unique challenges to implementation and collection of information about care quality. By providing an environment within and managed by the ED that allows sufficient time for enhanced care, beyond a 4-6 hour ED visit, protocol-driven ED Observation Units (EDOUs) would mitigate many identified challenges and promote better utilization of existing infrastructure. Further, it would enable patients presenting for overdose to remain in the ED long enough to receive their first dose of BUP prior to discharge. In the R61 phase, we will build on our existing clinical protocols as well as linked process and outcome measures of quality related to ED-initiated BUP and referral to be delivered during (1) a standard ED visit and (2) an enhanced ED visit in EDOU. Then, for the R33 phase, we propose a multicenter, randomized controlled trial in which patients with untreated OUD presenting to the University of Kentucky, NYU-Brooklyn (NYC), and Bellevue Hospital (NYC) EDs are randomized (1:1) to treatment though one of the two clinical protocols with outcomes assessed at the ED visit, 1, 3, and 6 months. We will evaluate processes and outcomes granularly to inform the development of reliable, valid measures using data that could be captured without undue burden. We will compare the relative effectiveness of the two approaches on the proportion of patients who receive ED- initiated BUP and referral, are linked to formal OUD treatment within 7 days and engaged in treatment at 30 days. We will assess changes in patient reported outcomes and drug use, and conduct an economic evaluation from a third-party payer perspective. Linking structural and process measures to population-level outcomes will allow us to guide and define quality improvement to inform accountability and policy. Evaluating the associations between patient-level characteristics, measure completion, and outcomes will help identify population needs and apply strategies to improve quality and reduce disparities.